The long term goal of this project is to investigate the functional correlates of mutant protein expression in the working heart. Using the technique of cardiac-specific transgenic overexpression, it is now possible to replace the contractile protein isoforms specifically in the cardiac compartment and thereby establish the functional consequences of the mutation over the lifetime of the animal as it is subjected to various external and internal stimuli. SPECIFIC AIM 1 will create an animal carrying a mutated myosin binding protein C (MyBP-C) that has been shown to cause familial hypertrophic cardiomyopathy, in order to determine whether such a mutation results in decreased cardiac function at the motor and fiber levels and whether an animal model of the disease can be created. SPECIFIC AIM 2 will test the hypothesis that replacing the ventricular form of the essential myosin light chain with a genetically engineered species will lead to an animal with enhanced cardiac function. The amino terminus of the essential myosin light chain is hypothesized to play a major role in determining contractility. A mutated essential light chain, lacking part of the "tether" region which is believed to slow down the cross bridge cycle, will be used to replace the endogenous species in the ventricles and atria. The cDNA will be linked to the cardiac-specific alpha-myosin heavy chain promoter and multiple lines of transgenic mice generated. SPECIFIC AIM 3 will study the dose-dependent consequences of mutant protein expression by analyzing multiple lines in which the degree of replacement varies, in order to understand the physiologic and pathogenic consequences. Changes will be measured at the molecular, biochemical, cellular, structural, whole organ and animal levels in order to directly establish the consequences of replacements. SPECIFIC AIM 4 will attempt to rescue genetically defined cardiomyopathies by breeding them into a background that has intrinsically enhanced cardiac function. These models will explore both the basic structure/function relationships of the contractile proteins, and should result in animals with enhanced and compromised cardiac function that will be generally useful in understanding the roles these processes play in both compensation and heart failure.